@article{NUMA_1974__22_132261,
     author = {F. Natterer and B. Werner},
     title = {Eine  {Erweiterung} des {Maximumsprinzips} f\"ur den {Laplaceschen} {Operator.}},
     journal = {Numerische Mathematik},
     pages = {149--156},
     publisher = {mathdoc},
     volume = {22},
     year = {1974},
     zbl = {0268.35029},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1974__22_132261/}
}